title: Genetic study of diabetic retinopathy: recruitment methodology and analysis of baseline characteristics.
abstract: BACKGROUND
  Diabetic retinopathy (DR) is a blinding disease of increasing prevalence that is caused by a complex interplay of genetic and environmental factors. Here we describe the patient recruitment methodology, case and control definitions, and clinical characteristics of a study sample to be used for genome-wide association analysis to detect genetic risk variants of DR.
  
  
  METHODS
  One thousand six hundred sixty-nine participants with either type 1 (T1) or type 2 (T2) diabetes mellitus (DM) aged 18 to 95 years were recruited in Australian hospital clinics. Individuals with T2DM had disease duration of at least 5 years and were taking oral hypoglycaemic medication, and/or insulin therapy. Participants underwent ophthalmic examination. Medical history and biochemistry results were collected. Venous blood was obtained for genetic analysis.
  
  
  RESULTS
  Six hundred eighty-three diabetic cases (178 T1DM and 505 T2DM participants) with sight-threatening DR, defined as severe non-proliferative DR, proliferative DR or diabetic macular oedema were included in this analysis. Eight hundred twelve individuals with DM but no DR or minimal non-proliferative DR were recruited as controls (191 with T1DM and 621 with T2DM). The presence of sight-threatening DR was significantly correlated with DM duration, hypertension, nephropathy, neuropathy, HbA1C and body mass index. Diabetic macular oedema was associated with T2DM (P < 0.001), whereas proliferative DR was associated with T1DM (P < 0.001).
  
  
  CONCLUSIONS
  Adoption of a case-control study design involving extremes of the DR phenotype makes this a suitable cohort, for a well-powered genome-wide association study to detect genetic risk variants for DR.
authors.affiliation: Department of Ophthalmology, Flinders University, Flinders Medical Centre, Adelaide, South Australia, Australia.
authors.forename: Georgia
authors.initials: G
authors.lastname: Kaidonis
authors.forename: Sotoodeh
authors.initials: S
authors.lastname: Abhary
authors.forename: Mark
authors.initials: M
authors.lastname: Daniell
authors.forename: Mark
authors.initials: M
authors.lastname: Gillies
authors.forename: Rhys
authors.initials: R
authors.lastname: Fogarty
authors.forename: Nikolai
authors.initials: N
authors.lastname: Petrovsky
authors.forename: Alicia
authors.initials: A
authors.lastname: Jenkins
authors.forename: Rohan
authors.initials: R
authors.lastname: Essex
authors.forename: John H
authors.initials: JH
authors.lastname: Chang
authors.forename: Bishwanath
authors.initials: B
authors.lastname: Pal
authors.forename: Alex W
authors.initials: AW
authors.lastname: Hewitt
authors.forename: Kathryn P
authors.initials: KP
authors.lastname: Burdon
authors.forename: Jamie E
authors.initials: JE
authors.lastname: Craig
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D016022:Case-Control Studies; D003922:Diabetes Mellitus, Type 1 / Q000150:complications; D003924:Diabetes Mellitus, Type 2 / Q000150:complications; D003930:Diabetic Retinopathy / Q000235:genetics*; D005260:Female; D005451:Fluorescein Angiography; D059647:Gene-Environment Interaction; D020022:Genetic Predisposition to Disease; D055106:Genome-Wide Association Study; D006442:Glycated Hemoglobin / Q000378:metabolism; D006801:Humans; D008269:Macular Edema / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D018579:Patient Selection; D055815:Young Adult
chemical_list: D006442:Glycated Hemoglobin; C517652:hemoglobin A1c protein, human
keywords: diabetic macular oedema; diabetic retinopathy; genome-wide association study